Airplanes operating in the northern hemisphere are frequently forced to function in a wide variety of climatic conditions, including snow, sleet, and freezing rain. When these climatic conditions cause the adherence and build-up of "ice" on the flight sustaining and controlling (aerodynamic) surfaces of an airplane, disaster becomes a likely prospect. Adherence and build up of "ice" (or dirt) on the fuselage of the airplane, while not as directly critical to flight performance as build-up on the aerodynamic surfaces, is also undesirable because of the weight and drag added to the airplane by such build-up. Accordingly, the prior art has provided systems which attempt to deal with these undesirable phenomena, at least while the airplane is on the ground, by subjecting the airplanes to "protective treatments" which either remove, or prevent--more properly, delay--the formation of, ice on the airplane prior to take-off. These "protective treatments" typically comprise the application, more or less uniformly across the major, including aerodynamic, surfaces of an airplane, of protective compounds comprising at least de-icing, and possibly also subsequent anti-icing, chemical compounds, preferably in the form of liquid sprays.
As illustrated, for example, by U.S. Pat. No. 4,378,755, more recent and advanced airplane protection systems are more or less automated and also recognize both the inherent waste and environmental risks resulting from the uncontained application of liquid chemicals to the airplanes. Accordingly, additional drainage and sump--or collection--systems are provided as an adjunct to the spray application systems to both re-cycle, and prevent ground contamination by, any excess spray.
Moreover, the system of the '755 patent also recognizes the possibility of providing a plurality of structures to allow the application of a plurality of different compounds to the airplane. However, despite the sound principles underlying such prior art systems, they still lack certain essential features which would greatly increase their effectiveness and utility and hence decrease their costs.
For one thing, because none of the prior art protection systems known to the applicants enclose the entire airplane, i.e. protect the airplane with a cover, during the application of the "treatment", an inevitable effect is the dilution, if not also contamination, of the protective compounds--if contained and collected--by the elements, such as rain or snow. More seriously, the lack of cover over the protective compound application stage continues to expose the airplane to the very elements against which "immunization" has just been attempted. In the face of this continued exposure, the prior art has simply been tempted to use the brute force of approach of either "more compound", or "more compounds". That is, because de-icing compounds have a limited "holdover", or protective, effect after application, continued exposure of the airplane to the elements--whether due to lack of cover and/or time lag between compound application and take-off--requires the application of either excessive de-icing, and/or subsequently applied anti-icing, compounds that delay (rather than eliminate) the formation of ice. Neither alternative is without adverse consequences, especially the application of anti-icing compounds.
Anti-icing compounds, known generally as "Type II" fluids, function in a significantly different manner from de-icing compounds, known generally as "Type I" fluids. Type I fluids, which typically comprise a more or less concentrated, aqueous solution of ethylene or propylene glycol, exhibit a viscosity characteristic that essentially allows them to drip-off the stationary airplane after application. Type II fluids (also nicknamed as "Gorilla Snot" in the trade) on the other hand, have an additional gelling agent added to a typical Type I formulation so that continued adherence (as suggested by the nickname) to the airplane surfaces is possible to thus delay the formation of ice while the airplane is on the ground. As the airplane accelerates for take-off, the applied Type II fluid rapidly loses viscosity and is essentially "stripped" off the airplane once an air speed of about 100 knots is reached.
The variable viscosity of Type II fluids described above, otherwise known to those skilled in the art as the variable reaction to the varying shear stress as a result of the velocity gradient across the Type II fluid surface, immensely complicates the nature of the systems required to apply these fluids. Because the viscosity change, once it occurs, is irreversible, Type II fluids have to be "gently squeezed on" so as not to expose them to a level of shear stress which renders them unusable. As if this weren't enough, Type II fluids are also much more hostile, i.e. corrosive, to the equipment used to apply them, so that uniquely dedicated, corrosion resistant, application systems utilizing stainless steel have to be employed. Finally, because the velocity required to "strip" the airplane of the applied Type II fluid is on the order of a minimum of about 100 knots, smaller airplanes which normally do not require such high rotation velocities, may be forced into an operating region closer to the boundaries of their performance envelopes when Type II fluids have been applied to them. In short, Type II fluids have enough significant disadvantages that their us becomes desirable only as a last resort.
Accordingly, it is a prime object of this invention to provide an airplane protective system which uses less chemical compound, and which may even, in certain circumstances, entirely eliminate the need for type II fluids.
A system which serves merely to protect airplanes against the adverse effects of cold weather phenomena would have--even in the northern hemisphere--only a limited, seasonal utility. This seasonally limited utility in turn leads to greatly increased "life cycle" costs because the total cost of a system can only be recovered over a greater length of time.
Accordingly, it is another object of this invention to provide an airplane protection system which has functions and capabilities allowing such system to be used year round for purposes other than merely airplane protection, such as, for example, washing, or routine, maintenance. The washing of airplanes is a highly desirable maintenance function contributing to the increased aerodynamic efficiency of, and consequently lower fuel costs for, the airplane.